As law enforcement officials continue to search for a motive in the Christmas Day explosion in Nashville, analysts are turning their attention to a related and seemingly significant question. When Anthony Warner blew himself up in his RV, he created one heck of a blast. The explosion was big enough to damage pretty much every building on an entire city block. I’m sure there was quite a bit of room inside that recreational vehicle, but it wasn’t that big. So what kind of bomb did he create that was capable of generating such destruction?

Some experienced blast investigators from the FBI have been reviewing the publicly available photos and videos and have reached a rather startling preliminary conclusion. They are describing Warner’s bomb as being “unique in the annals of” improvised explosive devices used by terrorists. If they’re correct, Warner would have had to have pulled off a very tricky design to create any sort of significant explosion. Also, they suggest that if we want to learn more about how he did it, officials should be looking for his test sites because there was no way he could have made it work on the first try. (Daily Beast)

Find his test sites, top bomb experts say.

Anthony Quinn Warner’s device, although probably made of common over-the-counter components, is unique in the annals of mayhem, according to seasoned FBI bomb experts consulted by SpyTalk.

“We’ve never seen an improvised thermobaric device before in this country or any country,” says Dave Williams, who conducted the FBI’s on-scene investigations of the World Trade Center, Oklahoma City, Pan Am 103 and Unabomber bombings, among other notorious incidents.

I wasn’t familiar with the term “thermobaric” prior to this. Thermobaric explosions are produced using the oxygen in the surrounding air to accelerate the rapid ignition of large quantities of gaseous fuels such as evaporated gasoline, propane, methane, acetylene or natural gas in an enclosed space. It’s the same principle that’s found behind stories of houses exploding when there’s a gas leak inside. But according to these demolition experts, the process is extremely tricky, particularly in a smaller space such as the inside of a vehicle. The mixture of air and fuel has to be exactly right to generate a truly massive blast. Too little fuel and you’ll only produce a rapid flash of flame that blows itself out. Too much and there won’t be enough oxygen to allow for all of the fuel to combust.

That’s why they’re saying that Warner must have practiced multiple times to learn how to get the mixture precisely correct and maximize the power of the explosion. He clearly couldn’t have been practicing at his house. We’ve seen pictures of that home and it’s in a fairly dense suburban neighborhood. Somebody would have eventually noticed a bunch of gas explosions and called the authorities. We already learned that Warner’s ex-girlfriend had tried to alert the police to the fact that her boyfriend was building bombs. Perhaps she knows where he was practicing? I’m going to assume that the FBI has asked her about it by now.

So how did these experts conclude that Warner used a thermobaric bomb to begin with? Their first clue was the rapidly expanding yellow and orange fireball, which is typical of a gaseous fuel-air explosion. Another factor they cited was how “clean” and efficient the combustion was, initially producing almost no smoke. There was some smoke later from burning tires and other debris, but if the RV had been packed with something like ammonium nitrate fertilizer and fuel oil (as was used in the Oklahoma City bombing), the fuel itself would have produced a massive cloud of smoke in addition to the blast. The same would be true if Warner had used dynamite or other conventional explosives. They produce more of a shockwave of force and plenty of smoke, but not so much of a fireball.

The FBI analysts interviewed for this report seem to suggest that Warner’s task was made even more difficult by the need to build a timer that would ignite the air and fuel mixture at precisely the right moment. But is that really true? Warner was sitting in the RV when it went off. If he was able to obtain some sort of piece of equipment to monitor the levels of gas in the back of the vehicle, he could have ignited the cloud manually when it reached the optimum level. That would also have allowed Warner to switch over from his recording warning of an imminent explosion to Petula Clark’s 1964 song “Downtown” just as the gas levels were approaching the needed concentration. (That’s still one of the weirdest parts of this story.)

While the science behind this is all very interesting, the depressing part is that Warner may have opened the door to other would-be domestic terrorists who may be considering attempting the use of thermobaric explosive devices in the future. If you can beat the problems of fuel concentration and managing the timing of the ignition, the required materials are very common and harder to track than true explosives or unusually large purchases of fertilizer.